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RTC Information

The MitySOM-A10S family of System on Modules (SoM) feature an on module Real Time Clock (RTC) IC to ensure the ability to maintain precision timing information while running and, if enabled by an external battery, while a unit is powered off.

RTC Device Part Number

The current RTC device used on the MitySOM-A10S family of modoules is the Abracon AB-RTCMK-32.768KHZ.

Abracon AB-RTCMK-32.768KHZ Datasheet: https://abracon.com/Precisiontiming/AB-RTCMK-32768kHz.pdf
Abracon AB-RTCMK-32.768kHz Application Manual: https://abracon.com/realtimeclock/AB-RTCMK-32.768kHz-Application-Manual.pdf

RTC I2C Interface on

  • The RTC device is accessible on the I2C0 bus of the MitySOM-A10S HPS
  • It is located at address '0110010' (0x32)

Linux Kernel Drivers

The driver name is rtc-ab-mk-t3.c, which can be found in the socfpga-4.9.78-ltsi kernel branch hosted by Critical Link. Link to driver source: https://support.criticallink.com/gitweb/?p=linux-socfpga.git;a=blob;f=drivers/rtc/rtc-ab-mk-t3.c;h=74e6280892ae14fb38e70c025cfd380300cb46e0;hb=refs/heads/socfpga-4.9.78-ltsi

Battery Backup

The "VBAT" input to the AB-RTCMK device (pin 8) is connected to J4G (pin G38) through a diode-or. If no VBAT is present, the RTC is powered by 3.3V through the diode-or from the module while power is supplied.
There is no battery installed on the MitySOM-A10S module itself. If battery backup of the RTC is desired a battery/circuitry must be added to the carrier board.

VBAT Current Draw:

With the battery installed on the deb board and powering the RTC we have measured current draws as follows:

Measured Min: tbd
Measured Typ: tbd
Measured Max: tbd

Based on IDD2 from the application manual the average max current from the AB-RTCMK device is about 2 uA and the typical current draw is 0.6 uA.
The typical maximum diode or leakage current is 100nA.

Battery Life

The battery life will be dependent upon the cell size used, operating temperatures, self-discharge rate of the battery and configuration of the RTC device.

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